Manufacture of electric heaters



Patented May 22, 1945 DANUFACTUREOF ELECTRIC HEATERS .Edwin L. Wiegand, Pittsburgli,lPa., assigne;` lto vEdwin L. Wiegand Company, Pittsburgh,` Pa.,

a corporation of 'Pennsylvania Application December-12,1940, Serial No. 369,164 A 15 claims. (01.226423) y My invention relates to the manufacture of electric heaters, and more particularly to'the manufacture of electrical heating elements comprising a resistor disposedwithin and insulated from a tubular metallic sheath. The principal object of my invention is the provision of newvand improved methods of producing such, electric heaters and the provision of. new and improved apparatus for carrying out such methods.

In the drawing accompanying this specification, and forming a part of this application, vI have shown, for purposes of illustration, one form which my invention may assume, and ln this drawing: f

Figure 1 is a brokenside elevation of appa`V ratus embodying my invention with which is assembled a sheath to be filled,

Figure 2 is a Vertical sectional fragmentary View, enlarged, of an'upper portion ofthe assembly shown in Figure 1,

Figure 3 is a vertical sectional fragmentary view, enlarged, of a lower portion of the assembly shown in Figure l,

Figure 4 is a section taken on the line 4'4 of Y 25 Figure 2, and y Figures 5, 6, and 7 are enlarged sectional views taken on the linesr -5, 6-6, and 1--1 respec-` tively, of Figure 3.' d

Referring to Figure l, there is here shownapparatus embodying my invention, comprising' a supporting means 20 which includes a Vertical'standard 2 I lmounted on a base 22. The base`22 may be fastened to table 23 with which maybe associated a vibrator indicated by the legend. `Secured to the vertical standard 2| in'anysuitable Way are arms 24, 25 which-may includeor serve to support V-clamps 26, 21 adapted to rigidly clamp andhold in an approximately vertical position a metallic tube or sheath 23. The tubular sheath *'28 may be of any sectional area,` size, or shape,"so long as it is adapted to end-illling vwith comminuted insulating material. In the illustrated embodiment it is shown as of circular crosssectional shape. The parts of eachV-clamp 26, 21 are adapted to be drawn together by means voi. screw bolts 29 and cooperating ywing nuts 30. 'Plug' means 3| has its upper end disposed in the opening at the'lower end of the sheath 28 and the lower end of the plug means3| may be disposed in the neck 3?. of a reservoir or flask 33, the reser-` voir having a nipple 34 connectable to a conduit 35 which is desirably reinforcedand flexible, and connected through any suitable `valve means to any suitable vacuum pump (not shown), al1 for purposes hereinafter to be described. As c will sheath 28 and parts of the apparatusl associated hereinafter more fully appear, a resistor 36 is disposed within the sheath 28 and `is held atone terminal end by the plug means 3| and at-the other terminal end by an anchor rod 31, the anchor rod being tightly adjustably held in avsuitable clamp 38-tightenable by a nut 33, the clamp 38 being in turn secured to the'vertical standard 2|. Means 4!) for introducing'comminute'd electricalsinsulating material into the sheath 28 'is provided, this means, in this instance, including what may be termed a filler tube -or a lead tube 4| insertable in the sheath 28, the leadtube 4| carrying at its upper end funnel means 42 fromwhichcomminuted insulating material may `flow into the lead tube 4|.

, InfFigure 2 is shown the upper portion of the therewith, and in Figure 3 is shown the lowerA portion of the sheath 28 and parts of the appa-fv Y ratus associated therewith. Referring-rstto Figure 3 the lower end of the sheath 28. is disposed within a collar 43 extending upwardly from f y the body 44 of theplug means 3|, thelower end of the sheath ZB'abutting the'shoulder 45 at 'the bottomy of the collar 43. The plug means 3| irl--Y cludes means for preventing comminutedinsulating-material `from being discharged from' the' lowerend of the sheath 28 while` at the same time permitting-'discharge of air through this means.

In the illustrated instance this means comprises a plug-member 46 the lower end of whch-iltsand is fastened in a central cylindricalj hole l'41 r through the body 44 ofy the plug means,nthe' hole 41 being of thesamev diameter and registering with the vopening at the lower end of the'sheath v28, The plug member 46 yis provided with aeplu-v rality of longitudinally extending air passages 49, desirably equally` circumferentially spaced. The plug member 46 is conveniently made of pin-v ion rod so `that the teeth provide the plurality of circumferentially spaced longitudinally extending passages 43. It is of course evident that the outer peripheral surface of the plugmember 46 lits slidably into the' insidesurface of the sheath 28.- The upper end of the plug member 46v has fastenedthereto what may be termed a iilter disc 5|)` provided with a plurality of circumferentially equally spaced small-holesv 5| of -the same number as the passages 49.I The disc 50 slidably iits the inside surface of the sheath 28 and isffastened to the upper end ofthe plug member 46, so that the holes 5| register with, in this instance, the radially inner end portions of the passages 49. The disc 50 is provided witha central aperture y52 registering with and of the-same size as a cen- 28, or both the lead tube 4| and the particular funnel means 42 may beomitted, and, in general, comminuted insulating material maybe fed into the sheath byjany other suitable means or in any other suitable way.

If desired, the sheath 2s may be tapped, to

`By reason ofthe provisioncf the vacuum at the of' insulating material comprised in an aggregater which under prior practice included particles varying from 4 0 mesh to 200 mesh. My invention obviates this objection'ev'en when liner material is used as will appear. Furthermore, theupward air currents, present without my invention, may be in the nature of air bubbles which rise rst at one side of the bore of the sheath and then at another side, or the uprising air may be otherwise non-uniformly and varyingly dis-Y tributed over the cross-section of the bore of the sheath, thereby causing an irregular distribution of the insulating material, so `that the lling is not uniformly dense around the resistor 36.

Besides obviating the difliculties and disadvani -tages caused by upwardly moving air currents,

my invention, by leliminating these upward air currents and causing instead a down-draft within the sheath, Vresults in further advantages.

For example, more uniform density and greater density of the iilling is obtained because the smaller particles tend to be sucked into the voids between the larger particles.

Also, assuming that'the resistor 36 is in the form of a helical coil, the insidebfthe coil is caused to fill -up more completely and uniformly due to the down-draft and suction, particles being` drawn into the inside of the coil through the adjacent convolutions thereof.

Furthermore, myr method enables the use of more finely ground insulating material. For example, I may use comminuted material of 60 mesh, and this material may include all fines normally produced by grinding mineral material of the type useful for electric heater purposes, including even the fines of 400 mesh. Fines of a size smaller than 400 mesh may be removed.

under some circumstancesbut this is not in general essential. M Orenely ground material may be used with my vacuum method inasmuch as the suction and down-draft makes a finely ground material flow downwardly in the sheath, whereas such material would not be free flowing in the absence of the provision of4 a vacuum. The use of more nely ground material enables a more dense lling to be made. Also, this results in economies in the use of material, inasmuch as the relatively finer particles need not be removed from the ground aggregate, or at least not to as great an extent as they have been prior to my method. For example, in the case of ground fused magnesium oxide, under prior practice, the fines below'a Certain maximum, which are removedfines available for use, they must be reprocessed asby re-fusion and comminution, to bring the particles to a desired larger size.

Also, I am enabled with'equal facility toA use an aggregate comprising smaller maximum size particles, because the necessity for making avail# able the too fine material by'expensive re-fusing and re-grinding is not involved, whereas, on the other hand,'particles in the ground material which are larger than desired may be easily re-ground.'

Furthermore, the provision of my' vacuum lling method increases the speed with which thel sheath may be lled, while at the same time enabling a more dense filling to be provided, the density being enhanced due t0 the use of ner materials. Greater density of the material before the usual compacting of the heating element, as by swaging, side pressing, or otherwise working the sheath, is desirable because, among other things, there is provided a greater amount and weight lof insulating materialf within a given space, thereby supplying a better insulating coat for the resistor with less necessary reduction of the sectional area of the heating element.

In addition, my vacuum lling method enables the manufacture of a tubular or rod type of heating element having a greater maximum of resistor within a given space a`nd also a greaterA fohmic resistance within a given-available space. Also, with a given cubical and dimensional limitation it enables the use' `of a resistor made from resistance wire, for example, one totwo sizes larger, for a given heating element the resistor l of which is to have a given total resistance, thus providing a much stronger resistor with a much greater area for a specified wattage rating.

At the beginning of the filling process, the static vacuum required is not Very high, but will increase as Athe level of the insulating material accumulated` in the sheath rises. The amount of air which is drawn through the plug means 3l may readily be regulated inany suitable way so as to allow, at any static vacuum, as much or more air' to be abstracted downwardly than is displaced by the incoming comminutedinsulating material.

I have found that when the sheath 28 has become iilled, in accordance with my vacuum meth- I cessfully used with od,` so that the insulating material completely embeds the resistor and a desired portion of the termina 6| within the sheath, a very substantial vacuum still is available at the upper end of the sheath, withl a vacuum of about l0 to 13 pounds inthe reservoir, even though the sheath is four.

feet long and onlyabout s of an vinch inside diameter, using comminuted insulatingmaterial of'100`% -60 mesh including 20% `-200 mesh. Accordingly, even ner materials, for example, such as hereinbefore referred to, may be sucthismethod. The foregoing figures and examples are given to illustrate better whatmay be'accomplished and not by way of limitation.

The lead tube kthereof rises. In this case the fins 64 only serve unavoidable in the grinding of the material, must j, be more or less removed. In order to make these 4! may be used very advan` tageously without the use of a vacuum at the' sion thereof. .Y l ,e i

o I am aWareJOf-a loris 'known and used way y.oi

posi-tively te `tentrel-.ly 'the resistor-iwliilenf the. resstorworiflf hence-.less esteosiori* sister 36 is relatively' fris,:.t iot1lessfemi'vv elsoiiiiloeetin a .resistorrwhih involves the use of e tub .hating er1-internal bere aseleselyos permis-.

sible iittiiie the ksiieiiieter of; the heliool resstorl 0 the inside `sulfate or the sheethoiid' the tube Alie e located in the sheath, byv external 1 lei-room,fer,entiitlfly speeed fins or projections ori the tube. 1n this instante the oomminiited insulate to be located thisy tube' bovine .en outside surface Asintesi f ine material `is introduced between-,the outside .0f

the .tube and the inside .of the slleittli.,` and. Clue l tothe characteristicsy oif type of lliiis. ab rangement; and due to the` relatively coarse Cqmminute. material :necessary to `loe. .used therewith tosecure freeiiow conditions, considerable cleareral movementl at alocal longitudinal zone which represents only a very small part olft length of the resistor, it being requi resistor istol be restrained against lateral ment. -to restrain it only Where the insultiiigj k materiel isfbui-ldioeineroundit o .Frein the' 'foregoing itwill be apparent eemminuted insulating material reduced .o the upper end of the lead'tube 14| v"has Heede-, ss

, not lonly to the outer periphery ofthe resist ,r

2o ance is necessarybetween the outsideends .of thel l l lfins or projections and theinsidef-Sllrfae of the sheath,v and considerable clearance isv necessary .minutecl material has theopportuni-tyfto build upbetween'the inside surfaceof the tubeand ^the outside :surface of the helical resistor. so that the cause, among ,other reasons, the mi tance between the resistor andthesh reduced, and the maximum electrica e l heating element is measured bythe electrical 4the routside surface of the' resistor and v'the inside ing -lodged therebetween.

the lead tube which maybe as little as about 0,l6 of A'an iinch'or even less. The outside surface ,of

surface 'of the sheath 28 snugly, Vfriction between than frictio'nbetweena lead tube and a resistor,

y and any friction which mayopposerelative-move-` 1 ment of the outside surface vof `the lead tube.4,|-

and the' inside-surface of the sheath 28 maybe objectionable results. Furthermoreiwith ra lead tube -4I accordance-'with 4my invention, Aprovided with fins 64 as hereinbefore;described, the fins .closely Acontact circumferentially spaced outsister, v:the areas of contact being very small.

1 Thus verylittle or no lateral movement of theresistor at the zone .of the iins is possible. The

finsy are -very'thin knife-like members, of a thickt as the thickness ,of the wall of the lead tube 4|, 3 or thinner, and the :edges of the fins may if de` l sired be yrounded or sharpened, as indicated, still further vto reduce the areas of contact so that these ,areas are not much more than points.Y Ac-` A' .cordingly,imovement .of the fins 64 along the re'f ermost surfaces of the convolution of the re- `ness,fin the illustrated instance, about the same 1'25 possibility 'or jamming of, these surfaces is resione its enti-re length out may enter intoy the sideof the` helical resistor between vthe .convo tions thereof. ,This is true also all the longituldinal zone defined bythe ns 64'.' .Hence theeomeflicientlyfnot only outside of the helical resistor but inside thereof,` since the ne particles have more opportunity to pass between the con-Volu-v `1 duced. Owing to` these necessaryclearances, contions to lthe inside of 4the resistor coil; even Athoughthe convolutions may `belof less extended siderable llateral displacementof Vtlie resistor is'v able to take place, which isueryobjectionable be-` i,

. alue cfa j surface of the lead tube, if vnot complete jamming f y of these surfaces due to larger particles, becom- *A lead tube in accordance with myA in ention y obviates these objections `and provides additional i r advantages, for the following reasons. The nl side surface of the lead-tube 4| risspaced a, dis;

tance :from the resistor coil 36 which is almost A `as great as the distance from the outer periphery 1 of the coi-l to the' inside surface of thek sheath 2,8,- -being less only bythe thicknessv of-the vwall of the lead tube 4| may be made to t theinside i these/surfaces being' of muchless :importance l readily overcome and, also, will not have any pitch. This effectis `accentuated when the lower endof vthe sheath 23 is subjected ytoa vacuum.`

In this case lif the Vspaceoutside..of the .resistor '36 tends to llup a little faster rthan the `space inside of the resistor; the vacuum causes a cone centration Of the down-draft in resistor.

If the lead e ltion of the comminuted material isfdesi-red .than

the inside of the is obtainable by merely allowing thematerial td flow into the sheath, or by icoinpacting it by vibrar tion, or by subjecting the lower end ofthe sheath f to avacuum, or yby both vibration and vacuum,A` then under anyrof thesev conditions the lead tube' s may be manuallynor mechanically-v repeatedly raised a desired amountand brought; down `again so as to tamp the commi-noted mlaterialas it acT cumulates and the level vbuilds up, or, :in general, relative reciprocal motion between the lead :tube 4| `andtlfiesl'ieath maybe created by manually or mechanically 4moving eitherthelead tube 4| or the sheath 28, 4so as to proyidedesirable Vibrae tion and Vtamping action; Ifdesired the lead tube 4| maybe rotated as tamping proceedabut YAthat is not essential. The relievedA or Vrrounded lower corners 615 of the ns may aid in forcing thecom.-

minuted material between the convolutions into the inside of the essential. f

vWith or without-subjecting the lower end of the sheath 28 fto avacuum, the base 22, and hence the entire' apparatus, may be longitudinally-Ver.- tically reciprocated or yibrated, `whereby the lead tube 4| -will be gradually forced upwardly 'by the resistor ,35, but that is not comminuted material as fastas eomrninuted ma,

terial finds its way under the end of the lead tube 4| and thens G4..- f

From the foregoing it .will be apparent-that While the vacuum iilliiis method and leedtube herein disclosed mutually cooperateto produce new results, the vacuum kfilling method-.in itself produces new results and may `be used without a lead tube or with other Aforms oflead tubes, and the disclosed lead tube inA itself `produces new ne- .sults and may be used without the vacuum iililing method, .and that the .commmuted indelen-nemer terial may or 'may notte tainted. 'and that the bekv tube 4| is used and ...more compact,`

sheath or apparatus carrying itfmayor imay not be tapped or vibrated. i i.

It will be understood that after the filling o`peration of the heating element has been completed and the element has :been removedfrom the filling apparatus, the spacefleft by the plug means 46 may be filled with any desiredv suitable insulating material, and the same is true with respect to any space left at the other'end ofthe sheath. t

It will be apparent that the resistor 36lmaybe made' of any desired suitable material,J and of any desired suitable form; that the insulating materialmay be granular, comminuted or powdered,

or any form permitting `practice of the. disclosed f process, and that it is desirably refractory and heat-conducting and may be, or may include, for example, silica, or silicates, or magnesium oxide, or aluminum oxide, orany refractory oxide or combination of refractory oxides, or anyother suitable refractory material, desirably of a mineral character; and that thesheath 28 `may be seamless or seam-welded tubing made of a metal or metal alloy capable of withstanding temperatures of from 1200 F. to 1600 F. or higher or of any material capableof withstanding Whatever temperature of operationmay be selected.

From the foregoing it will be apparent to those skilled in the art that the disclosedv embodiment of my invention provides for newandfimproved manufacture of electric heaters, and accordingly,

of said resistor, andthe longitudinal ends of said fins having relieved marginal corners. y y

4.- Apparatus for use in introducing comminuted electrical-insulating material endwise into a tubular sheath toembed a resistor disposed in said sheath, comprising; a ller tube adapted to accomplishes the principal objectibf my invention. On the other hand,v it alsovwill begobvious to those skilled inthe art that the disclosed embodiment of my invention may` be` variously changed and modified, or features thereof, singly or collectively, embodied in other combinations than those disclosed, without departing from the spirit of my invention, kor sacricing all of the advantages thereof, and that accordingly, the disclosure herein is illustrative on1y and my invention is not limited thereto.

1. Apparatus for use `in introducing commi-y nuted electricalinsulating material endwise into a tubular sheath `to lembed a resistor disposed 'inl said sheath, comprising: a filler-'tube adapted to slidably fit the inside surface of said sheath; and a plurality of longitudinal iinscircumferentially spaced on the inside surface of said filler tube, said ns extending radially: inward and being adapted to slidably to engage peripheral surfaces of said resistor. i Y

2. Apparatus for use -in introducing.` comminut-ed electrical-insulatingmaterial endwise into a tubular sheath to embed a resistor disposed -in said sheath, comprising: a' iiller tube adapted to slidably t the inside surface ofv said sheath; and a piurauty of longitudinm sns circumferentiauy spaced on the inside surface of saidjiiller tube, said ns extending radially inward and being adapted to slidably engage peripheral `surfaces of said 'resistor in a longitudinal zone [of engagement which is relatively short with respectV to the length of said resistor.

3. Apparatus for use in introducing' commi-4 nuted electrical-insulating materialfendwise into a tubular sheath to embed a resistor disposed in said sheath, comprising: a filler tube adapted to slidably t the inside surface of said sheath ;'y and a pluralityof longitudinal fins circumferentially slidably lit the inside surface of said sheath; funnel means communicating with said filler tube and constructed and arranged for feeding comminuted insulating material into the upper end of said ller tube; and barrier means, disposed within said funnel means above the outlet thereof, constructed and arranged to control the flow of comminuted insulating vmaterial from yabove lsaid barrier means into the' space above said outlet, said barrier means comprising a barrier tube and a member having a central aperture ting said barrierv tube and having a plurality of circumferentially1 spaced perforations.

5. Apparatus for use in introducing comminuted electrical-insulating material endwise into a tubular sheath to embed a resistor disposed in l said sheath, comprising: a filler tube adapted to slidably fit the inside surface of said sheath;

funnel means communicating substantially yairtight with'said fillery tube, said funnel means having an outlet coaxial with said ller tube', for feeding comminuted' insulating material into the upper end of said ller tube; means whereby a lower part of the space Within said sheath may be subjected to a desired vacuum; means substantially preventing discharge of said material While permitting withdrawal of air; and barrier means disposed within said funnel meansabove the outlet thereof, said barrier means having passage means for permitting now of commi# nuted insulating material from above said barrier means into the space above said outlet and beiner so lconstructed and arranged-'that said space is substantially sealed except for` said passage means. a

6. Apparatus for use in introducing comminuted electrical-insulating material endwisexinto a tubular sheath to embed a resistor disposed in said sheath, comprising:A ya'iller tube adapted to slidably t the inside lsurface of said sheath; funnel means communicating lwith said ller tube, said funnel means having an'outlet coaxial with saidller tube, for feeding comminuted insulating material into the upper end of said filler tube; perforated vbarrier-xme'ans, disposed Within said funnel means above the outlet thereof, constructed and arranged to control the flow of comminuted insulating material from aboveA said barrier means into the space above said outlet; means, including a rod spaced from the margin of'said outlet and extending freely therethrough, constructed and arranged to support said resistor;r and said barrier means having Wall means providing an elongated aperture coaxial with said outlet, said rod extending through said aperture, said barrier means being so constructed andarranged that said wall means prevents the entrance of insulatingl material between said wall means and-said rod.

7. Apparatus for use in introducing comminuted electrical-insulating material endwise into a tubular sheath to vembed a resistor disposed in said sheath, comprisinga filler tube adapted to slidably fit the inside surface of `said sheath; funnel means communicating with said filler tube,

said funnel meanshaving'anoutlet coaxialy with'` said ller tube, for-feeding comminuted insulating material into the upper .end of said ller tube ;k

" said barrier means.`

funnel means above the outletthereof,"construct red and arranged to `control the lflllni'rkoi."com rnil 'nuted insulating materialvfrom 'above said barrier means intoethe space above said outlet; means,

perforated barrier means, disposed' withiny sai-d x including a rod spaced from the margin of said outletand vextending lfreely therethrough, conf'- x structed andv arranged'to`Sllp1`20rt said resistor; e and said barrier means l includingtubular :means coaxial with said outlet, said rodV extending` through 'saidl tubularjineans.

'niited electrical-insulating nl'aterial`-'e'ndwisev into a` tubular sheathfto'enibc'd aA resistor ldiSADQSIe'd*in said sheath, comprising: av ller tube adapted .to siidbiyytfthe Yinside 'rfaoe of said sheath; iuniiei'fiieans communicatingsubstantially airtight with said iilier tube', said funiioimoans vhayiney aiij ouder` ooaxiai `with said vfingir tooo, vfor fee 'g insulating material into the @Per 'er1-deinem@ ller tube: Amemes .whereby e i ff Cif` Lthe Sp'aeelwithie Said ,Sheath may; r

be su Jected -to aV desired vacuum;A meansy sub-1- vst'eirltfl'llff ,pretenties @geleerde iQf Said material W'lefblfntn Y.llfi'elldr@Weil.v of air; perforated oarri'er meansrdisposed within said; funnel means Illalalled to support saidresistor; and said f barrier means having wall means providingan elongatedraperturecoaxialwith said outlet, said lodvextending through `said aperture, rsaidbarrier lilfllfms beingI so .constructed and arranged that said wall.. means, prevents rthe entrance of insu-` lating material between said vvvfallmea'ns and said rod, and substantially prevents the entra-nce of airfrom atmosphere through the space between Asaid Wall means and "said rodfinto 'the space below 9. `vApparatus for. use in-f i introducing come minuted ,electrical-.insulating material endwise into atubular .sheath to-iemb'edf aresistor disposed l i in saidsheath, comprising-*.meansconneetable'to theendsv of said-resistor,-constructedand-arranged Lto., position saidnre'sistor spaced from the` Ainside surface @of saidsheath; vmeans -for *intro-1' du ng comminuted Ielectrical-insul'ating .material ill .all'l ,uplldllld ofzsaid sheath; and meansl Wllleby aplwelppartofthe;space within s'a'id sheath mayhbesubjeted, toa desired "vacuum,` comprising/a1 i/acuuirrreservoir` receptacle havlan apertiire, Aplugmeans, havingL yanV end l'sheath toa desired vacuum; thus to' rinovetle air from among the particles of' the! material Within ftheshe'ath; '-egress'of said' material while' `permitting 'such substantially preventing withdrawal of the air; and engaging saidvlfielic'al resistor,y at circ'umferentia113gy spaced' points only, toA restrain said resistor against lateral movement atleast at approxiinateljr thelevel ofA the insi'ilatel ing material accumulated in saidsheath. lli

11. Apparatus for use in introducing comminuted electrical-insulating material endwise into s i a tubular sheath to'embed a resistorlvdis'posedin s said sheath', ccmprisingz'rsupportin'g 4means; means, carried by said-'supporting meansIcon'- structed and 'arranged to' hold said sheath" in an approximately vertical position; means connectable toA the ends of said resistor andv carriedb'y saidl supporting means, constructed and arranged' to"positio'nsaid resistor spaced from thefinside surface of said sheath; means for introducing comminuted electricaleinsulating rnaterial into the upper end of said sheath; means substantially preventing discharge of said material; said inaterial introducing means comprising a filler tube insertable in said sheath and freely movablevup and down therein, and funnel means communiv eating withsaid iiller` tube .and constructed and arranged for' feeding comminuted insulating ina` e nuted eectricaleinsulating"material endwisev into a tubular sheath tov embed- `a "resistor disposed in 'extending ,freelyy therethrough, constructed,

- ment of said portion is permitted; means wherey by a` lowerpartof the space within said sheath;

adapted `"count in,' s,alidfape1tl,lre the other end of l said Aplug means, being adapted -to` lit in the lower passersV and means wherebysaid'rooeotaoie' may bo ,oon-,i

nected to nie'an's 'fcreii'haustingiair from' said receptacle.

k10. The method or prodcinga ytiiloiiiair i@metric heating element, which comprises: arranging a tubular sneatnf'iii'an, Aapproximateiy vertical position; v'disposir'ig'a helicalvresistor"longitudinally in 1 n saidfsheath'intoposition'spaced'transversely from theinside surface of said sheath';"progressively introducing, comminute'dj v`electrica`l-insulating materiaiintothe upper leiid fisaidfsheath while s siibj'eotifig--a iower perror-the space withinsaidit l means in r.operativeg, ,posi-tieni;k means lear terial into the .upper ena or said nner tube, p

12. Apparatus for use in 'introducing commisaid sheath, comprising: first means for siidamy engaging the inside surface of saidsheath "so as to be positioned within said "sheath by said inside surta-ce; second means positioned by andl below said nist means and having a portion for siidabiy engaging andjpo'sitively positioning said resistor with respect to said inside surface at the zone of engagement; said' rst means 'beingv "so construct'- ed and arranger-l that `access of said insulating ina-l terial to said resistor above thefzofn'e of engage- *substantially 'preventing "discharge Jof said -materialwhile permitting 'withdrawal of air, j

Apparatuszfori-use 'in introducing comminuted electricaleinsulating 1 material endwisefinto a tubular vmetallicxsheatlr :toembed :a resistor-dis-` posed in saidffsheath andhaving Ia terminal "at its i.

lower end, Comprising.: filler .means for. introducing comminuted electrical-insulating materialin-f to theppper end- 0f ,thesheathrplug meansadapted to be inserted'v end wise" into, the `lower end of the `vSheath Mesi-red distance, haring an aperture for Areceivingsaid terminal of lsaid-resistor, and having airrpassage means extending throushsaid smemeans from ene .end thereof to; the other;

means t0 slipserteaideller meanwnd'sai plus by Seid plus @eerie ferjifssteiiine. Seid, ferifiel "te" saidrplug meaijis;J and means `connected [to the 1 uter end of ysaid plugl means whereby 'airis 'from said sheath through 'said passage :means and and constructed and arranged to be disposed about and so spaced from said resistor and from said elongated member as to provide for lcngi` tudinal movement of said ller tube relative to said resistor and said elongated member, said filler tube being constructed and arranged to slidably fit the inside surface of said sheath; funnel means having an outlet communicating with said ller tube and constructed and arranged for feeding comminuted insulating material into the upper end of said filler tube; perforated barrier toa tubular metallic sheath to embed a `resistor disposed in said sheath and having an upper terminal, comprising: positioning means, including an elongated member connectable to the upper 4terminal of said resistor, constructed and ar ranged to positionsaid resistor vspaced from the inside surface of said sheath; a filler tube separate from said positioning means and constructed and arranged to be disposed about and so spaced from said resistor and from said elongated member as to provide for longitudinal movement of l said ller tube relative to said resistor and said elongated member, said ller tube being constructed and arranged to slidablyt the inside surface of said sheath; funnel means communicating with said filler' tube and constructed and arranged for feeding comminuted insulating material into the upper end of said filler tube; and means to support said positioning means, said nller tube,-

and'said funnel means, in operative position,

EDWIN L. WIEGAND. 

